The invention relates to a retaining cam for a rotatable fastener to connect components, with the retaining cam comprising a housing, which is pivotally supported on a base plate, by which the retaining cam can be connected to one of the components in a fixed manner, and into which a screw is inserted in a rotationally fixed fashion, onto which a fastener bolt can be screwed, rotationally connected to one of the other components, with at least one spring element being allocated to the screw for creating an elastic pretension for rotationally securing the fastener bolt.
A rotatable fastener of the above-mentioned type is a standard part in aeronautics and space exploration. The retaining cam of this rotatable fastener complies with the standard prEN 6092 of AECMA (The European Association of Aerospace Industries-Standardization, Brussels, Belgium, Edition P1, draft dated Mar. 22, 2004.) The fastener bolt of the rotatable fastener complies with the standard prEN 6088 of AECMA (Edition P1, April 2006.) Such rotatable fasteners are used in aeronautics and space exploration to transfer strong forces, for example a maximum tensile stress of 6300 N and a maximum shearing force of 11,000 N. These known rotatable fasteners are used in an aircraft, for example for a detachable connection of an interior cover panel or an access panel to the fuselage frame or a cell. The retaining cam is fastened via its base plate to the fuselage frame, for example via rivets. The fastener bolt is connected to an interior cover panel or an access panel in a rotational but captive fashion. The fastener bolt has a bore with a double-threaded internal thread. The screw inserted into the retaining cam in a rotationally fixed fashion has a double-threaded external tread. A perfect connection of the fastener bolt to the retaining cam can only be created in prior art when their axes are aligned to each other, e.g., when two components to be connected to each other are parallel in reference to each other. Such alignment of the axes or the parallel positioning of the components may already be difficult due to permissible tolerances per se. During the assembly, the fastener bolt will pull the retaining cam, which is pivotal to a certain extent in reference to the base plate, against said base plate. When the axes are not aligned to each other, the retaining cam will attempt to pull itself with its circular contact area, which encompasses a facial opening of its housing facing the fastener bolt, against the base plate, with the retaining cam attempting to align said contact area to the base plate parallel in reference to the fuselage frame. If the axes fail to assume a perpendicular position in reference to the fuselage frame tensions can develop in the rotatable fastener, because the retaining cam will not contact the base plate over its entire area. This insufficient contact can even lead to the housing of the retaining cam, which is embodied relatively thinly, becoming damaged. Furthermore, there are applications in which curved interior cover panels shall be fastened at the fuselage frame. Previously, particular expenses incurred to appropriately position the fastener cams at the frame side for a screwed connection to the fastener bolt, prevent the occurrence of the above-mentioned tensions or the above-mentioned damage of the housing of the retaining cam. Additionally, particular expenses are necessary for the retaining cam to contact the base plate with its entire contact area, within permissible tolerances, when screwed to the fastener bolt. This is even further aggravated in that such rotatable fasteners are designed for frequent reusability. Commonly such a rotatable fastener should withstand 1500 screw cycles.
Quarter-rotation fasteners are known (for example from the catalog Alcoa Fastening Systems, 2007), in which the above-mentioned difficulties are avoided such that the retaining cam is connected via the base plate to the fuselage frame or the like in a stiff fashion and that a fastener pin is inserted, which at its frontal end comprises a Phillips pin. During fastening, the Phillips pin of the fastener pin glides over a ramp of the retaining cam and after a quarter rotation reaches a catch position, in which it is held by the elastic pretension of a spring element. Such a rotatable fastener shows a simple design and can easily be assembled; however it is only useable for considerably lower tensile stress applications.